Fuse link



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April 16, 1935. E. F. BOOTHE FUSE LINK Filed April 29, 1933 PatentedApr. 16, 1935 UNITED STATES PATENT QFFWE Application April 29, 1933,Serial No. 668,558

6 Claims.

This invention relates to fuse links for high voltage electricalprotective apparatus, and more particularly to fuse links of so-calledtension type.

Fuse links of the type referred to above are those which are adapted tobe held under a mechanical tension produced by means of a spring whichforms a part of the protective apparatus, the purpose being to create awide gap between the severed ends of the fuse after the same has becomeruptured by abnormal current, and to quickly extinguish any arcattending the blowing of the fuse by causing the ruptured fuse ends tofly apart under the action of the spring tension.

A heretofore prevailing difiiculty inherent in tension fuses,particularly those of low, or fractional ampere current carryingcapacity, results from the tendency of the fuse to become severed byreason of the mechanical forces applied thereto, or if not actuallysevered the application of such forces to the link for a long period oftime results in an alteration of the operating characteristic, or ratingof the fuse link. For example, it has been determined that an unstressedfuse wire which is intended to become ruptured upon the passagetherethrough of currents in excess of, say, three-fourths of an ampere,when held under a mechanical tension of the order produced by springmeans found in the usual types of pro tective apparatus, are ruptured bycurrents of a magnitude substantially less than the figure specified.However, the operating characteristics of the fuse link are notmaterially altered when only relatively small mechanical forces areapplied thereto. It will appear obvious that the forces which arepermissible for a particular fuse depend upon its mechanical strengthwhich, in most cases, is a function of the current carrying capacity ofthe fuse. However, since it is customary to provide protective devices,each of which is adapted to accommodate fuse links in a wide range ofsizes or capacities, the link tensioning means ordinarily produceexcessive strains in fuse links of the smaller capacities.

To overcome this undesirable feature, I have provided, as an object ofmy invention, a fuse link construction, especially applicable for fusesof low current carrying capacity, resulting in an improved link whichwill not be harmfully affected by the application thereto of relativelyhigh mechanical forces.

Another object of my invention is to provide, in a device of thecharacter described, improved means for relieving the fusible element ofa predetermined fractional portion of the forces produced by thetensioning means.

A further object of my invention is to provide improved means operablewhen the fuse blows to cause the ruptured ends of the fusible element tofly apart with multiplied velocity.

These and other objects and advantages will appear from the followingdescription and accompanying drawing, in which:

Fig. 1 is an en arged plan view of a presently preferred embodiment ofmy invention; Fig. 2 is side elevation of the construction illustratedin l Fig. is a elevation of my improved device as installed in a fuseswitch, and Fig. i is a sectional view taken at the line .4 of Fig. 1.

My improved fuse link consists in a bar of insulating mate ial, near theends of which are mounted terminal members, one thereof beingpermanently fastened to the bar, and the other being mounted to permitof its movement along the bar in a direction away from the fixedterminal when a current conducting fusible element interconnecting theterminal members becomes ruptured. The fuse device embodying myinvention is especially designed for use in apparatus having means forapplying mechanical forces to the terminal members referred to above,which forces tend to move the terminal members in relatively oppositedirections. Such apparatus is exemplifled in Fig. 3 of the drawing.Under normal operating conditions, relative movements of the terminalmembers tending to increase the distance therebctween is prevented bythe connecting fusible element which, obviously, is placed undertension. It will appear, however, that only a definite predeterminedfractional part of the force tending to separate the terminal members isapplied to the fusible element, and that the remainder of such force ormechanical load is carried by the insulating bar.

Describing the device of my invention in greater detail, referencenumeral t l designates the insulating bar, preferably formed of fiber.Secured at one end of the bar by means of a rivet i i is a metal plate52 constituting a terminal member, the rivet ii, in the present example,also serving to connect a wire conductor 52 to the terminal member I2.The outer end of wire it may be provided with a metal button or contacthead M (Fig. 3).

The opposite end of the bar H3 is preferably shouldered as indicated atl 5 to form a tongue l6. Disposed in overlying relation with the tongueI 5 is a projecting portion or tongue 8? formed on a metal plate 18constituting a second terminal member. The tongue portions [6 and I? areengirdled by a metal band or collar l9 which produces a substantiallyrigid connection between the bar it] and the terminal 16, but which inno wise prevents movement of the terminal l8 along the bar H! in adirection away from the terminal 12. Such movement, however, is normallyprevented by a fusible element 20, consisting of a wire or filamentwhich is adapted to become ruptured by the fusing of solder joiningtogether two component parts of the element when current ofpredetermined magnitude is passed therethrough, the soldered junctionbeing indicated at A. One end of the element 26 is soldered, orotherwise suitably fastened to the fixed terminal B2. The elementextends from the terminal l2 to an aperture 2! in the terminal 58,through which aperture the element passes. On the opposite side of theassembly the element extends backwardly toward the terminal 12 to anaperture 22 in the bar It. After passing through such aperture, theelement extends again to the terminal I 3 where it may be fixedlysecured, or if desired the filament may be passed through a second setof apertures 23 and 24 in the terminal and bar respectively as shown,prior to its ultimate securement to the terminal 58. Thus, it willappear that the bar it and terminal i3 are substantially laced togetherby means of the fusible element 2G. The apertures 2 l, 22, 23 and 24, bypreference, are free of any sharp corners which would tend to out theelement 29, and are sufficiently large to permit the filament to movefreely therethrough, which movement, as will hereinafter be explained,occurs when the element becomes ruptured. A conductor 25 has one of itsends attached to the terminal 18 and serves to connect such terminal toa spring or other tensioning means on the switching apparatus.

Such apparatus is exemplified in Fig. 3 and for purposes of completenessmay bebriefly described as follows: The device is provided with aremovable fuse cartridge 26 through which the fuse link of my inventionextends, the contact head M of the link engaging one end of thecartridge and the conductor 25 projecting through the opposite end ofthe cartridge which is preferably open. A spring 2'! associated with theswitch terminal assembly, designated generally at 28, is adapted toengage the conductor 25 of the fuse link and hold the link undertension, the stressed position of spring 2'! being shown in full lines,and the relaxed position of such spring being shown in broken lines. 7 7

From the foregoing description it will appear that I have provided afuse link of tension type which will safely withstand mechanical forcesof magnitude substantially greater than the forces required to break thefusible. element, and yet which device retains all of the desirablecharacteristics of a tension link. In other words, a device constructedin accordance with the present invention employing a fusible elementhaving tensile strength of, for example, ten pounds may be safelyinstalled in a switch or cut out having tensioning means adapted toexert a force of between 40 and 50 pounds. This desirable featureresults from the fact that the tensioning forces are not applieddirectly to a single strand of the filament constituting the fusibleelement, as is customary in heretofore prevailing devices, but that suchforces are equilibrated by a plurality of filament portions arranged inmultiple relation. In accordance with certain well known principles ofmechanics governing the operation of simple pulley systems, whichprinciples also apply to the device of my invention, only a fractionalpart of the forces exerted at the ends of thefuse link will be impartedto the fusible element. Further, when the filament becomes ruptured bythe passage of abnormal current, the ruptured ends will fly apart withmultiplied velocity, a feature which is conducive to a rapid clearing ofthe line protected by the device of my invention.

Having described my invention with reference to a single presentlypreferred embodiment thereof, I realize that certain changes may be madein the structure herein shown and described without departing from thespirit and full intended scope of my invention as defined by theappended claims.

I claim:

1. In a fuse assembly of tension type, an insulating bar, a terminalmember fixedly positioned on said bar and a terminal member adapted fordisplacement longitudinally of said bar, a fusible element connectingsaid terminal members, said fusible element having a section thereoflooped about portions of said bar and said last named terminal member.

2. In a fuse link, a pair of spaced terminal members, an insulatingtension strip extending between said members, and a fusible elementhaving its ends connected to said terminal members, said fusible elementhaving a looped portion of at least one full turn normally interlinking,and preventing separation of said tension strip and one of said terminalmembers.

3. In a fuse device, an insulating bar, a terminal member mounted formovement along said bar, a terminal member spaced from said movableterminal member and fixedly secured to said bar, a fusible conductorinterconnecting said terminal members and having portions thereofextending transversely through said bar and said movable terminalmember.

4. In a fuse device of the tension type, relatively separable terminalmembers, a bar of insulating material extending between said terminalmembers, one of said terminal members being engaged by, and adapted formovement along said bar, a conducting element'having a fusible section,electrically interconnecting said terminal members, said element havinga looped portion forming a linking connection between one of saidterminal elements and said bar.

5. Ina fuse device of tension type, spaced, relatively separableterminal members, an integral bar of insulating material extendingbetween, and engaging said terminal members, a current conductingelement electrically interconnecting said terminal members, said elementhaving a looped portion normally preventing displacement of one of theterminal members endwise of said bar, and means permanently securing theother of said terminal members to said bar.

6. In a fuse link of tension type, a bar of insulating material, aterminal member fixedly secured to one end of said bar, a displaceableterminal member nearthe opposite end of said bar, means constrainingsaid displaceable terminal member for movement endwise of said bar, anda fuse wire interconnecting said terminal members, said fuse wire havinga looped portion extending through said displaceable terminal memher andbar, and normally preventing 'endwise movement of the displaceableterminal member relative to said bar.

' EUGENE F. BOOTHE.

